There is a need in the electronic equipment industry to make convenient and secure electrical connections between an array of electrical terminals and a set of small side-by-side terminal pads, such as the terminal pads of a printed circuit board or a liquid crystal display. A promising technique for making such connections is taught in laid-open United Kingdom patent application No. 2,048,582A, which teaches an adhesive connector tape comprising a flexible nonconductive backing carrying a pattern of longitudinally electrically conductive stripes or conductors, each covered by a band of electrically conductive adhesive. Between each pair of conductors and conductive adhesive bands is an insulative adhesive. FIG. 1 of the U.K. patent application shows the use of a length of the tape for multiple electrical interconnection between two sets of terminal pads, the tape being anchored in position through the combined effect of the adhesive of the electrically conductive adhesive bands and the insulative adhesive between those bands.
The U.K. patent application suggests that the electrically conductive adhesive bands may be a resilient conductive epoxy made commercially available by Micro-Circuit Company of New Buffalo, Michigan. Such an adhesive would afford bonds to glass plate having a shear strength far in excess of 20 kPa, preferably at least 10,000 kPa.
The U.K. patent application teaches that the conductors are applied by silk-screening, brushing, roller coating, spraying or dipping and that the bands of electrically conductive adhesive are applied directly over these conductors. No matter how carefully the adhesive bands are applied, there inevitably is a degree of meander at the edges so that no edge of an adhesive band precisely follows an edge of the underlying conductor.
It is believed that the meander would make it commercially impractical to produce the U.K tape having conductors closer than about 0.5 mm center to center. Even at about 1.0 mn center to center, it would probably be necessary for each adhesive band to be wider than the underlying conductor to assure a sufficient conductivity through the adhesive band at any point along the conductor.
U.S. Pat. No. 4,113,981 (Fujita et al.) uses an adhesive layer for electrically interconnecting two facing arrays of electrical conductors. The adhesive layer includes spherical conductive particles of substantially the same thickness as the adhesive, thus providing a conductive path through each particle that bridges facing pairs of connectors. The particles are randomly distributed throughout the adhesive layer, but the Fujita patent indicates that if the particles comprise less than 30% of the volume of the layer, they will be sufficiently spaced so that the intervening adhesive will insulate against short circuiting between laterally adjacent connectors.
U.S. Pat. No. 3,475,213 (Stow) discloses a pressure-sensitive adhesive tape having an electrically conductive backing and an adhesive layer which contains a monolayer of electrically conductive particles like the adhesive layer of the Fujita patent.
U.S. Pat. No. 3,132,204 (Giellerup) shows an adhesive tape having two conductive paths, which would provide multiple connections.